Because Compare uses threads, we need to make sure it is finished when a
compare is executed from the command line. This was a problem for command
sequences, because the next command would start running before the compare
was done, and the buffer with differences was available.
So this commit adds the "run-blocking" parameter when using
LFUN_DIALOG_SHOW to run a Compare. When calling Compare with run-sync, the
LFUN will wait for the compare worker thread to finish before returning and
possibly running the next command.
In particular, the directory frontends/qt4 is renamed to frontends/qt.
Many configurations file have to be updated. All mentions of qt4 in
the source have been audited, and changed to qt if necessary.
The only part that has not been updated is the CMake build system.
